Coronation Street's Roy Cropper, played by David Neilson, Fiz Stape, played by Jennie Mcalpine and Tyrone Dobbs, played by Alan Halsall, try to encourage the ailing Hayley Cropper, played by Julie Hesmondhalgh, to eat some fruit

It's Julie's last day on Coronation Street and it's only lunch time, but there have already been tears.

"Jennie [McAlpine, who plays Fiz] got me going with her card," says Julie Hesmondhalgh, who's played Hayley Cropper for the last 16 years.

Her departing storyline's been one of the most talked about in soap history, not only because she and husband Roy (David Neilson) are such well-loved characters, but because of Hayley's controversial decision to end her own life after being diagnosed with terminal cancer.

Hesmondhalgh, 43, knew the moment she told the show's producer Stuart Blackburn she wanted to leave, that it wasn't going to be in the back of a taxi.

"It wasn't necessarily what I wanted, but I knew it had to be that way for Hayley and Roy," explains the actress. "It wouldn't have made any sense to do anything else. Had I gone off to Africa [as the character did in 2007 when Hesmondhalgh had a break], I would've been ringing Roy all the time."

Blackburn, a former Corrie scriptwriter, was on his way home following his first day in charge, when he received the call.

"Stuart, bless him, doesn't mince his words at the best of times," say Hesmondhalgh, chuckling as she recalls their conversation.

"I said, 'Stuart, I can't couch this with any other term but I'm going to leave,' and he went, 'Oh my God!'"

Roy and Hayley were introduced by Alma Baldwin back in 1998, when Hayley was a shy shop assistant at Firman's Freezers. A friendship ensued and then, on one of their dates, Hayley revealed that she was a pre-operative transgender formerly called Harold (she later underwent sex change surgery).

"Right at the beginning, the trans community weren't happy with the storyline because, to be fair, it was a bit of a joke," says Hesmondhalgh, who's wearing a bright green Sixties-style dress, her peroxide crop messily styled.

"But I never saw it as a joke. I read up on it, talked to people and tried to do it properly, and when David and I started working together, we both took it on. I think the trans community saw it and thought it was actually changing attitudes."

The pair had a blessing ceremony in 1999, which is where Hesmondhalgh met her husband-to-be Ian Kershaw, the writer and actor who played "a baddie journalist" in the episode.

Then in 2010, Roy and Hayley got married to reflect the change in law. "Roy gave a speech, which remains one of my favourite lines ever," says Hesmondhalgh. "He said, 'We've remained the same, the world has turned to meet us'. And that's exactly what happened. They've just carried on their little path and the world has adjusted, and that's brilliant."

Looking back, she thinks it's ridiculous that the soap chose an actress to play the role.

"Now you'd have a trans actor, but the pressure for someone would've been off the scale back then."

The Lancashire-born star's initial interest had been social work. She decided later to focus on acting, studying at LAMDA before joining an independent theatre company. Roles in The Bill, Dalziel And Pascoe and The Dwelling Place followed, before Coronation Street came calling.

Just as Hayley's arrival proved thought-provoking, so does her departure – in choosing to end her life before her cancer treatment renders her incapable of doing so.

A member of the British Humanist Association, Hesmondhalgh has "quite strong views" in favour of pro-choice. For that reason, she's always understood Hayley's decision, while Neilson hasn't.

"We as actors have very different views, so he's just played what he feels and I've just played what I feel."

"My relationship with David's been the absolute best," she adds. "He's completely different from Roy. He's very dry, he doesn't suffer fools. He's so loved and respected."

Viewers won't actually see Hayley die but they will witness her drinking the lethal concoction, which Roy tries to dissuade her from doing right up until the end.

The last scene was done in one take.

"The director, Kay Patrick, was keen for us not to have to keep doing it, because when you first do a scene like that, it's very raw and you get the performance."

While the last few months have been tough-going, Hesmondhalgh's keen not to complain. "I always think you've got to be careful when you're talking about things like this, because I don't actually have it [terminal cancer]," says the actress, who mulled over her decision to leave for a long time before making the announcement.

"I'd started thinking about it [leaving] when I was doing a play at the Royal Exchange Theatre [in Manchester] last year," she notes. "I just felt, if I didn't do it now, I never would. Sometimes you've got to shake things up."

She'll continue watching the soap – "Oh God, totally!" – but she may have to set the recorder, as she's starring in the new play Blindsided, followed by Black Roses, which she's taking to London on tour.